1. Field of the Invention
The invention relates to a device and a method for determining and controlling the bale length on a pick-up baler for agricultural harvested material, wherein the device comprises a pick-up device, a conveying device, with or without cutting device, arranged downstream of the pick-up device for conveying the harvested material to a feed channel, a conveying action for the harvested material that is controlled as a function of the degree of filling of the feed channel for conveying the harvested material from the feed channel into a pressing channel by means of a feed stroke, a pressing piston arranged within the pressing channel and movable in a reciprocating fashion for compacting the harvested material, as well as a tying device for tying the finished bale with tying material.
2. Description of the Related Art
Such pick-up balers are used to generate primarily rectangular large-size, high-density bales of stalk material. It is particularly important in this connection that a uniform preset bale length is maintained for transport and storage of the bales and for a possible precise determination of the harvest yield.
Several patent applications with proposed solutions for different devices for determining the bale length are known. In most cases, the length is determined by means of a measuring wheel that is embodied as a thumb wheel and is driven by the moving bale; it measures the bale length directly by a mechanical device or an electronic sensor connected thereto. After reaching a preset nominal value, the tying of the bale is triggered. In all these measuring devices, the precision of repeated measurements of the bale length is however unsatisfactory. Many factors regarding the material properties lead to different bale properties and behavior. In particular, the density of the harvested material and the restoring expansion of the bale have an effect on the measuring results because of slip and reverse rotation of the measuring wheel. A further imprecision of this bale length measurement action re-sides in that a bale growth is assumed for the last piston stroke of a bale that is triggered after the tying action has been initiated. However, this stroke, depending on the degree of filling of the pressing chamber, can actually vary extremely and, therefore, the bale length can vary also.
In the solution proposed in German patent 38 09 132 C1 for measuring the bale length, the aforementioned disadvantages of the direct length sensing on the bale by means of a measuring wheel are circumvented in that the stroke length of the pressing piston is used as a parameter for determining the bale length. In this connection, it is assumed that with each stroke of the pressing piston the achieved bale growth represents a constant value so that, based on this growth value per stroke and the number of strokes of the pressing piston, the precise length of a bale can be determined. Since the bale growth per pressing piston stroke is only a theoretical value and since is known in practice that harvested materials to be processed cannot be compacted to the same degree, this method of measuring the bale length is also not precise enough.